1. Field of invention
The present invention relates to removal of suspended solids, including resin and fatty acids from untreated or primary treated pulp mill effluents, including CTMP mill effluents.
The present invention will facilitate the treatment of pulp mill effluents by reducing or eliminating the input of suspended solids to the biological reactors and physical separation processes.
2. Description of Prior Art The presence of excessive amounts of total suspended solids (TSS) is detrimental to biological treatment of effluents, as has been observed in several treatment plants in Canada and Scandinavia. The suspended solids also interfere in physical separation processes employed in closed-cycle mill applications, namely evaporation, membrane filtration and freeze crystallization.
The principal methods for separation of solids from pulp mill effluents include: a) settling, b) flotation, and c) filtration. A number of studies have been performed on the conventional settling augmented by coagulation, in order to improve treatment performance. These studies included optimization of pH, temperature, retention time and the sequence of chemical addition.
O'Brian and O'Brien, in U.S. Pat. No. 4,115,188 discloses that acidification to pH &lt;4 followed by addition of calcium hydroxide to pH &gt;10 caused coagulation and precipitation of suspended solids from the paper mill waste water. Japanese patent JP 53,058,002, assigned to Sanyo Kokusaku Pulp, proposes acidification of the waste liquor and treatment with an anionactive polyacrylamide-based flocculent, to remove suspended solids. U.S. Pat. No. 3,959,129 describes a method for removing ink and suspended particles by treating the waste deinking effluent stream with ferric chloride and calcium hydroxide followed by vacuum filtration through a &lt;250 micron screen. Japanese patent JP 49,078,367 shows treatment of pulping waste effluent streams with magnesium chloride and calcium hydroxide to enhance settling rates. Japanese Patent 89,174,242 of Toyo Roshi KK, describes filtration of effluents through polyolefin, polyester and polyacryl fibers to remove suspended solids.
Kopylov, SU Pat. No. 981,233, describes a single cylinder flotation cell for removal of suspended solids from the pulp and paper industry effluents. Canzoneri, U.S. Pat. No. 4,782,789, proposed a double cell (concentric) process for removal of suspended solids.
Excess water from a paper machine vacuum filter savealls has been treated by a precoat filter to recover fibers (Lardieri, N.J. and J. W. Dappen, TAPPI. 50 (11), 125A (1967)). Pulp was used as the precoat medium and the recovered fibers, along with the precoat pulp, were bleached and used for tissue manufacture.
The above methods for treatment of waste streams from pulp and paper mills have several shortcomings, including (a) the use of expensive pulp as the filter medium in the filter, (b) no recycle of the precoat material or water, (c) limited removal of suspended solids, (d) large space requirements, (e) high capital costs, (f) production of dilute sludges that require dewatering before disposal, and (g) the need for chemical agents such as lime, alum and polyelectrolytes which, in addition to increasing the sludge volume, may be detrimental to the environment during sludge disposal.